1) Field of the Invention
The present invention relates to a belt driving controller, a process cartridge that includes the belt driving controller, and an image forming apparatus that employs the belt driving controller.
2) Description of the Related Art
Conventionally, an endless belt is wound on a driving roller and one or a plurality of driven rollers, and is driven by transmitting rotation of a drive motor to the driving roller via a drive transmitting member to rotate the driven roller(s).
A belt driving apparatus that includes the above mechanism is disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 2001-66909. In the belt driving unit, an encoding roll is attached to the driven roller in contact with the endless belt to generate a pulse in response to a speed of the belt, and the pulse is fed into a controller to control the drive motor.
With this scheme, since the endless belt is not wound on the driven roller, the driven roller is not influenced by fluctuation in thickness of the belt. However, there is a difficulty in controlling the belt driving unit well because it is not possible to completely remove a slip between the driven roller and the endless belt.
Some conventional belt driving unites include an encoder for each of the driving roller and the driven roller so that the angular speeds of both the driving roller and the driven roller are detected by each of the encoders to find a difference between the angular speeds. The difference is detected by an up-down counter, and the difference is superposed on a speed control system of the drive motor to perform a feedback control of the drive motor.
In the belt driving controller of this type, a belt winding angle on the driven roller to which the encoder is attached is made large so that the slip between the driven roller and the endless belt can be eliminated.
Such a technology is disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 2000-330353.
However, since the endless belt is wound on the driven roller, the driven roller is influenced by the fluctuation in thickness of the belt, and the angular speed cannot be accurately measured and controlled. Further, since the endless belt is similarly wound on the driving roller, the driving roller is influenced by the fluctuation in the thickness of the belt. As a result, the belt cannot be driven at a constant speed even when the driving roller is rotated at a constant angular speed.